Process for hydrogenating furfural



, Patented Apr. 20, 1937 v UNITED STATES PATE N'l OFFICE rnoonss FOR nrnRoGENATIiIG Wilbur Arthur Lazier, Marshallton, Del., assignor to-E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware.

No Drawing.

' 13 Claims.

This invention relates to processes for the catalytic hydrogenation of organic compounds in the liquid or vapor phase and more particularly to processes for the hydrogenation of furfural by means of chromite hydrogenation catalysts.

The application is a continuation in part of my copending specifications Nos. 456,298 and 456,299 filed May 2'7, 1930.

Considerable work has been done in the'field of catalysis with a view to developing efficient materials for the hydrogenation of such unsaturated compounds as the olefines, unsaturated fats and fatty acids, benzene and its derivatives, and a large number of other compounds containing unsaturated functions, such as the ultra-compounds, nitriles, and heterocyclic unsaturated rings. Most of this work has been based upon-the classical discovery of Sabatier that finely divided metallic nickel is capableof causing the union of hydrogen with these compounds. The method has been further expanded and supplemented by the work of Ipatief on the application of high pressures to these reactions. I

Extensive research has been carried out heretofore with the result that several difierent methods for the preparation of hydrogenation catalysts have been developed, the most common of which involve the precipitation and reduction ofnickel hydroxide or carbonate, reduction of nickel oxide prepared by ignition of the nitrate, anodic oxidation followed by reduction, heating to their decomposition temperature of certain organic salts of nickel, and electrochemical deposition of metallic nickel.

As is well known, these catalysts have found extensive use in the commercial Hydrogenation of fats, oils, and similar readily hydrogenated substances. I have found, however, that in gen- 40 eral catalysts prepared by the above methods, although ordinarily satisfactory for the hydrogenation of fats and oils, may be entirely unsuitable for the. more difiicult hydrogenation of.

such compounds as aldehydes, ketones, sugars, phenols, furfural and its derivatives, or benzene and pyridine and their homologues. Although furfural has been hydrogenated in the liquid and vapor phase by means of nickel catalysts prepared by reduction of nickel oxide and in the vapor phase by means of reduced copper, in so far as I am aware, the processes already described have not attained commercial success. Reduced nickel is sensitive to a variety of catalyst poisons while metallic copper succumbs to a sintering process caused by moderate heating which results in permanent loss of activity. I am not aware of any process in which chromite catalysts have been employed for the hydrogenation of furfural prior to my use thereof.

This invention, accordingly, has as an object 5 to carryout the catalytic hydrogenation of furfural by the use of highly efficient chromite catalysts. A further object is to provide a process for the hydrogenation .of furfural in either liquid or vapor phase by the use of highly efficient chromite catalysts prepared by heating or other- Wise reducing a chromate of a hydrogenating metal. It is a specific object to carry out the hydrogenation of furfural by the use of chromite catalysts derived from double chromates of hydrogenating metals and nitrogen bases.

These objects are accomplished by' the following invention, which in its general aspects, com prises the employment in the liquid or gas phase hydrogenation of furfural of catalysts prepared by reducing a salt comprising a combination or an oxide of a hydrogenating metal with an oxide of chromium to form an oxide composition containing chromium oxide of lower valence. This reduction may be effected by reacting with hy- 25 drogen at an elevated temperature, by heating or ignition alone, or by heating or ignition followed by reduction with hydrogen. The object of the reduction in any case is to obtain at least part of the hydrogenating component in the form of a finely divided and highly active metal or metallic oxide. Catalysts so prepared may be said to consist of a hydrogenatlng metal or its oxide, either associated or combined with chromium sesquioxide. By the term hydrogenating metal, I refer to a metal which is capable of causing the union of hydrogen with a compound capable of hydrogenation with or without the splitting off of water. Included in this group of metals are iron, nickel, cobalt, copper, silver, and tin.

' Inorder to classify the new catalysts under a generic term regardless of their method of preparation, they may be designated as chromite catalysts. However, by the term chromite I do, not intend to define these compositions as definite chemical compounds, but. as compositions in which the catalytically active component is a hydrogenating metal which may be either combined or otherwise closely associated with chromium oxide in a lower stage of oxidation. The hydrogenating metal may exist, either in the metallic form or as'an oxide, or both, the chemical relationships of the various elements of the composition depending to a certain extent upon the methods of preparation and reduction employed. 1

The specific nature and purpose or the invention requirethat the catalyst mass contain an 5 oxide of trivalent chromium associated or combined with a hydrogenating metal and/or metal oxide. Materials conforming to these conditions are suitable as catalysts for carrying out the process embodied within the scope of my invenion.

Taking the preparation of nickel chromite cat- 7 alysts as typical of the compositions of my invention, certain nickel-chromium compounds con- 7 stitute a convenient starting point from which to prepare efiicient hydrogenating catalysts according to the principles of this invention:

(1) Concentrated solutions of nickel chloride and neutral ammonium chromateare permitted to react at room temperature. Upon standing, a green crystalline salt of nickel ammonium chromate is formed. Thesolution is filtered with suction and the precipitate dried and heated slightly to start the decomposition reaction, which there after proceeds spontaneously with the evolution of sufiicient heat to leave a glowing residue prob- V ably consisting of combined nickel oxide and chromium oxide. This composition may be subsequently further reduced with hydrogen to produce the desired catalyst.

'(2) Two-molarsolutions of nickel nitrate and ammonium chromate are mixedv in equivalent amounts and heated to boiling, whereupon a brick red precipitate of basic nickel ammonium chromate is separated. Ammonia may be added to neutralize the acid solution formed by the precipi- The methods described above are equally ap- V plicable to the preparation of chromites of hydrogena-ting metals other than nickel, for example, other members of the ferrous metal group, such as those of ironand cobalt.

(4) Tin ammonium chromate may be prepared by treating a solution of stannous chloride and strong hydrochloric acid with ammonium bichromate and neutralizing the mixture with ammonia. After reduction, the tin-chromium oxide complex becomes active for the hydrogenation of such compounds as nitrobenzene.

preparation is formed bythe interaction of equimolecular proportions of copper nitrate and nor- .mal ammonium chromate solutions, followed by ignition. Basic copper ammonium chromate-is 05 formed by the precipitation, which yieldsa complex mixture of copper oxide and copper chromite on gentle ignition. This product is activefor the hydrogenation of furiural and other unsaturated compounds without further treatment, andis therefore a very convenient hydrogenation catalyst to prepare. As in the preparation of the nickel catalysts, the copper oxide-copper chro-,

mite catalyst may be further reduced with hydrogen to yield acatalyst mass containing metallic copper commingled with copper oxide'and copper (5) Similarly, a very active copper chromite chromite. The copper chromite catalyst, prepared by ignition of the double chromate, without having been subjected to further reduction by hydrogen is highly efllcient for the purposes or the invention.

I have disclosed above the preparation of chromite catalysts by the spontaneous decomposition ofdouble ammonium chromates. Bythe term nitrogen base, I include, besides ammonium compounds, organic derivatives such as salts of pyridine, aniline and methyl amine. When heated, these organic derivatives behave in a manner similar to the ammonium derivatives and yield chromltes, which, upon reduction, possess the same catalytic properties. Various formulae have been (NH4) 2N1 (CrO4) 2.6H2O

has-been assigned, while more dilute solutions at higherttemperatures give rise to the formation of a brick'red precipitate probably having the formula (NH4)2Ni(CrO4)2.2NH3. Both of these compounds decompose spontaneously on heating and yield a product in" which chromium is presv ent inthe trivalent form.

The nitrogen base compounds, typified by nickel I ammonium chromate, are preferably heated slowbut. in general,. it maybe said to range from 200 C. to 400. C. Reduction of the resulting composition with hydrogen may be carried out at 400 C.600 C., preferablyat 500 C.

The simplechromates, typified by nickel chromate prepared as illustrated in- (3), may be reduced to the chromite by igniting at a temperature somewhat higher than is required for the nitrogen base multiple chromates. Ignition of chromates of this type takes place at about BOW-800 0., although higher temperatures may' be used in -special cases. Where further reduction by means of hydrogen is desired, it may be efiected at about 400-600 C. and preferably at about 500 C. p a

It is possible to carry out the reduction of chroma-tes' of eitherof the above types by exposing them to the action of hydrogen at elevated temperature, without having submitted the material'to previous ignition. Thus catalysts may be prepared by subjecting the chromates to hydrogen at a temperature of 400600 C. for a period of time suflicient to convert the chromates into compositions containing either free are included merely for purposes of illustration and not as a limitation, disclose specific methods used in carrying the invention into practice and the improved results accruing from its use.

' Example 1 A nickel chromite hydrogenation catalyst was prepared as follows: A solution containing one water was mixed with another solution of equal volume containing one ,mol. of ammonium chromate. The mixture was heated to boiling and neutralized with additional ammonium hydroxide. The brick-red precipitate of nickel -am- 'monium chromate was filtered off hot, thoroughly washed, and dried. The precipitated chromate was then ignited at 400 C. for four hours to convert the chromate to chromite, after which it was reduced in hydrogen at 500 C. The reducedv catalyst contained the nickel partly in the elementary form and partly combined with the chromium oxide.

v Two hundred grams of furfural was shaken with 30 grams of water and grams of the above described catalyst at a temperature of 100'-140 C. and under a hydrogen pressure of 2000 lbs/sq. in. Hydrogen was absorbed rapidly, the reaction being complete in a few hours. The liquid product was separated from the catalyst by filtration and distilled. Over 60% came overat the correct boiling point for tetr'ahydrofurfuryl alcohol.

Example 2.

One hundred grams of furfural and 13 grams of water were shaken vigorously with 7 grams of a nickel chromite catalyst under 1400 lbs. hydrogen pressure and at a temperature of 80-110 C. The catalyst was prepared by the reduction of nickel chromate with hydrogen at 450 C.-500 C. Under the conditions described, the yield of tetrahydro'furfuryl alcohol was about 65%.

The above examples illustrate the hydrogenation of furfural in the presence of water. Water need not be used, however, its utility mainly residing in its tendency to decrease the conversion of furfural to high boiling compounds at the expense of the yield of tetrahydrofurfuryl alcohol.

Example 3 A copper chromite catalyst was prepared as follows: A two-molar solution of neutral ammonium chromate was added to an equal volume of a two-molar solution of copper nitrate with stirring at a temperature of 25 C. Ammonium hydroxide was added to neutrality to litmus and the precipitate allowed to settle. The liquor was decanted and the precipitate was washed 5 times by decantation with cold water, filtered, and dried at 110 C. The copper ammonium chromate thus obtained was ignited at 400 C. to drive ofi ammonia and oxygen, thereby converting the residue to a bluish black powder that has been characterized as copper chromite.

A mixture consisting of 15 grams of copper chromite thus prepared and 200 g. of furfural was shaken with hydrogen at a pressure of 1500 lbs./sq. in. and at a temperature of 175 C. Hydrogen absorption stopped after 2 hours. liquid product was found by distillation tocontain 6.! grams of .furfuryl alcohol, '75 grams of higher boiling material, and 13 grams of unchanged furfural.

The copper chromite catalyst prepared as described may, before use, he reduced with hydrogen at about 400 C. The resulting composition containing reduced copper, copper oxide, and copper chromite may then be used in the hydrogenation of furfural under the conditions given when the non-hydrogenated copper chromite catalyst was used.

" Emmpled 75 Copper chromite prepared as described in Example 3 was briquetted and screened to give 6-14 mesh granules. Twenty-five cc. of this granular catalyst was loaded into a small tube furnace and heated up to 200 C. in a slow stream of hydrogen. At this temperature and at atmospheric pressure 70 cc. of freshly distilled furfural was vaporized and passed over the catalyst with 36 liters of hydrogen during the course of three hours. The liquid products were condensed and separated from the excess hydrogen. By distillation there were isolated about 13 cc. of methyl furfurane and about 36 cc. of furfuryl alcohol, corresponding to conversions of about 18% and 45%, respectively; No tetrahydrofuriuryl alcohol was found among the products of the vapor phase hydrogenation of furfural' over the copper chromite catalyst.

The copper chromite, either before or after briquetting. may be subjected to a further reduction withhydrogen, as described in Example 3. The resulting composition may be substituted, under the operating conditions described in this example, in place of the copper chromite catalyst specified.

The catalysts referred to in the preceding examples are all characterized by the fact that they comprise or include a chromite of a hydrogenating metal. Thisis true not only of those catalysts prepared by simple ignition of a chromate but also of those catalysts which have been subjected to hydrogenation under the conditions specified herein. Hydrogenation either without prior ignition or subsequent to prior ignition of the metal chromates produces a composite catalyst at least a portion of which is a chromite.

It is apparent from the foregoing examples that the invention may be practiced as a vapor phase process wherein the catalyst is employed in a granular form and isheld stationary while a mixture of hydrogen and furfural vapor is passed over it, or it maybe operated as a liquid phase process wherein the catalyst is dispersed in a liquid medium which is agitated under hydrogen pressure to facilitate contact between liquid, solid, and gas. The liquid phase modification may be carried out as a batch or continuous operation. One satisfactory mode of operation is to pump the liquid furfural counter-current to a stream of hydrogen through a heated tower packed with catalyst granules.

In the liquid phase, hydrogenation may begin at temperatures as low as 50 C. Higher temperatures are preferred, however, for the increased rate of reaction obtained. The upper limits of temperature are conditioned'only by decomposition and side reactions which become serious at about 300 C. Pressures from atmospheric to several hundred atmospheres may be employed for either liquid or vapor phase operations, the upper limit of pressure being determined by the strength of the apparatus employed.

The nickel chromite catalyst when applied in the liquid phase hydrogenation yields either furfuryl alcohol or tetrahydrofurfuryl alcohol depending on the conditions but the latter product'- predominates. Copper chromite on the otherv hand, yields only the furfuryi alcohol from either liquid or vapor phase hydrogenation. In the vapor phase, methyl iurfurane is obtained as a icy-product. Itcan, however, be made the major product by a proper adjustment of the operating conditions.

The proposed methods of catalyst preparation have several advantages. Not only is the catalyst very active, but it is also more capable of withstanding catalyst poisons, such as oxygen and sulphur, than known types of catalysts. This is presumably because of the potential supply of unreduced hydrogenating metal which may be 5 continuously activated under the conditionsof hydrogenation. When badly poisoned the supporting oxide (for example, -chromium oxide) facilitates regeneration, which is brought about by gentle ignition. Another advantage is that the materials of this invention lend themselves very readily to compression into a form that may be 'used in a continuous operation wherein the liquid to be hydrogenated is permitted to flow over the contact mass in the presence of hydrogen under is pressure. Nickel and copper chromites, for example, are readily briquetted with the ordinary types of pharmaceutical tablet machinery without injury to the porosity or activity of the catalyst. It will be apparent that a continuous method of 0 operation employing the catalysts of this invention offers many advantages over the usual auto clave process.

As many apparently and widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

. I claim:

1. The process which comprises reacting hydrogen and furfural in the presence of a catalyst prepared by reducing a copper chromate to form a mass containing a substantial amount of copper chromite, at a temperature of from 70-300 C. and under a pressure of several atmospheres,

the furfural being maintained substantially in the liquid state during the reaction.

2. The process which comprises reacting hycatalyst comprising essentially copper chromite, the reaction being carried on at a temperature of 50 to 300 C., and under super-atmospheric pressure.

4. The process which comprises reacting hydrogen and furfural at a temperature between 50 and 300 C. in the presence of a catalyst essentia-lly comprising a chromite of copper.

5. The process which comprises reacting hyv drogen and furfural at a temperature between sentiailly comprising copper associated with chromium sesqui-oxide. l

6. The process which comprises reacting hydrogen and liquid furfural at a temperature between 50" and 300 C. in the presence of a catalyst essentially comprising a chromite of copper.

7. The process which comprises reacting hydrogen and furfural in the gas phase at a temperature between 50 and 300 C. in the presence of a catalyst essentially comprising a chromite of copper.

8. The process which comprises reacting hydrogen and furfural at a temperature between 50 and 300 C. in the presence of a catalyst prepared byreducing a copper chromate.

9. The process which comprises reacting hydrogen and furfural at a temperature between 50 and 300? C. in the presence of a catalyst prepared by reducing a double chromate of copper and of a nitrogen base.

10. The process which comprises reacting hydrogen and furfural at a temperature between 50 and 300 C. in the presence of a catalyst prepared by reducing copper ammonium chromate.

11. The process in accordance with claim 9 characterized in that the reduction of the catalyst is carried out by heating same to a temperature at which the valence of the chromium atom is reduced to a lower valence.

drogen and furfural at a temperature between 50 and 300 C. under superatmospheric pressures in the presence of a catalyst essentially comprising a chromite of copper.

- WIlJBUR A. LAZIER.

' 50 and 300 C. in the presence of a catalyst es- 

